The present invention relates to a navigation apparatus which displays on such CRT display a combination of both the route which a vehicle may take and the current position of the vehicle.
Generally, such navigation apparatuses have been designed to display map information stored in a large-capacity storage device, such as a CD-ROM, on a CRT screen. The map information may be the courses, names, distances and directions of roads, the places located along the roads, the locations and names of intersections, and the locations and names of buildings.
Navigation systems having means for receiving traffic information through the radio are also known. In such a navigation system, all the traffic information that can be displayed at that time is displayed on a CRT screen in accordance with data obtained by the reception means and from road information stored internally, which is called "internal road information". Such a navigation system is disclosed in, for example, Japanese Kokai No. 63-231477.
Since the purpose of the navigation system is to make the driver aware of the location of the vehicle on the screen, the vehicle position must always be displayed with a map image as background. Display of the vehicle position with the map image in the background may be done in any of the following methods:
(1): Firstly, the vehicle position is fixed to one position on the screen (generally, to the central position), and the background image is scrolled as the vehicle moves forward. This first method is in turn classified into the (1)-1 and (1)-2 methods:
In the (1)-1 method, the top of the display screen is fixedly directed to, for example, the north. The background map image scrolls in parallel with the direction of the marker/symbol of the vehicle. Although the marker is fixed on one position on the screen, it changes its direction to coincide with the actual direction of travel, and the background image scrolls appropriately coincident with the change in the direction of the marker.
In the (1)-2 method, the marker does not change its direction coincident with the change in the direction of the vehicle. However, the background map image moves in parallel and also rotates coincident with the actual movement of the vehicle.
(2): Secondly, a single-image section of a map is fixedly displayed with the top of the map fixedly directed to the north. The vehicle marker moves along the fixed image of the map until the vehicle reaches the edge portion of the map image. At that time, and thereafter, further non-scrolling sections of the map appear successively.
(3): In another conventional navigation system, when the destination is input on the map on the screen, the recommended to that destination is automatically chosen by the system, and displayed on the map.
(4): In still another system, the driver manually inputs the route which he or she will take, and that route is displayed.
Displaying both the route the driver will take and the current position of the vehicle is advantageous because the driver can recognize the current position of the vehicle along that route whose road and traffic information is the most important to the driver.
The navigation system which shows a combination of both the route and the current position of the vehicle generally displays only the route along which the vehicle moves forward. At best, it contains corners at which the vehicle may make a turn. Therefore, such a navigation system suffers from the following drawbacks. In the display method itemized by (2), as the vehicle position moves along the displayed route, the length of the route left gets shorter. Further it will eventually come to the end of the screen. At that time, there is no further display of the route, and the driver may not be able to recognize the current position of the vehicle. In the method (1), if the position of the marker/symbol of the vehicle is in the center of the screen, the length of the displayed route is about a half of the overall length of the screen, at most. This is disadvantageous from the viewpoint of effective utilization of the narrow display screen.